/Engine/Source/Runtime/Engine/Public/Net/OnlineEngineInterface.h
the stored nickname on the OnlineSubsystem for a player with a given unique id
virtual [FString](API\Runtime\Core\Containers\FString) GetPlayerNickname ( [UWorld](API\Runtime\Engine\Engine\UWorld) * World, const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & UniqueId )